1. Field of the Invention
The present invention relates in general to the field of roller-hearth furnaces and in particular to a roller for roller-hearth furnaces, said roller exhibiting a rotatable support body, a plurality of support disks mounted on the support body and, adjacent to the support disks, heat-insulated areas in each of which the support body is surrounded by at least one insulating layer of fibre material. Further, the present invention relates to a method for heat-insulating such a roller wherein by spray application of a fibre material at least one insulating layer surrounding an area to be insulated of a support body of the roller is created.
2. Prior Art
Such rollers have proved useful in practice. The heat insulation ensures that, on the one hand, the material to be heat-treated is not inadmissibly cooled and that, on the other hand, the support body of the roller is not inadmissibly heated. The support body can preferably be designed as an interior-cooled pipe.
A major difficulty lies in the fastening and mounting of the insulation consisting of fibre material. For example, from the DE-PS 37 40 620 and the DE-OS 40 41 217 it is known to provide the insulating layer with a jacket protecting and holding the fibre material together. However, with this method there is a danger of scale adhering to this jacket and growing until it has the same circumference as the rollers. This can lead to damage to the material to be treated. One at least equally serious consequence may be that the jacket breaks and the fibre material subsequently detaches itself. The roller must then be replaced immediately as otherwise the support body will overheat and be destroyed.
Further, the German patent application P 40 25 935.8 without prior disclosure describes a roller in which the areas to be insulated of the support body are surrounded by a fibre mat provided with needles onto which a fibre material is sprayed. The fibre material bonds with the fibre mat. Additional hold is provided by anchors which are fastened to the support body, penetrate the fibre mat and engage in the sprayed-on fibre material with flat clamping means. It has been found that this type of insulation does not stand up to the vibration loads occurring during operation. The fibre material increasingly detaches itself around the anchors, begins to crumble and finally falls off. Immediate maintenance work is also necessary in this case to avoid destruction of the support body.